Exporting procedurally textured models for game engine
Blender's node system cannot be exported since the 3D formats aren't able to store them and the game engines do not have nodes that are equivalent to the ones found in Blender.

What you need to do is bake your textures. Generally for game models you start with a high poly, detailed model from which you create the low poly version that can be used by the game engine (or several for different level of details - LODs). Part of the process is baking the normal map and PBR textures in order to get as close as possible to the look of the high poly model while keeping the polycount low. This is to ensure good performance of the game and keeping vertex budget for hero props (a building in the distant background doesn't need as many polygons as the model of your main character).